Astronomers from the University of Warwick, England, have discovered that an exoplanet often hailed as "Earth’s twin" is being continually bombarded by gamma rays and scorching plasma from its host star. The findings put into question the potential habitability of the planet, as life would be unlikely to develop and thrive in such harsh conditions. The research is published in the Monthly Notices of the Royal Astronomical Society.
The object, referred to as Kepler-438b, orbits in the habitable zone of a very active red dwarf star. The star emits huge superflares, each 10 times more powerful than the strongest solar flare recorded from the Sun. A superflare from this particular dwarf star is expected to have 5,000 times the energy of the asteroid that killed the dinosaurs.
The superflares generate powerful gamma rays, extremely damaging and penetrating radiation. If the flares weren’t enough, the dwarf is expected to produce large coronal mass ejections (CME), large eruptions of plasma from the surface of the star that can disrupt the atmosphere. This combination spells dire consequences for Kepler-438b.
“In the Kepler data, we’ve seen seven flares associated with coronal mass ejections. Each flare happened every few hundred days, and the continuous blasts might have led the planet to lose its atmosphere,” Dr. David Armitage, lead author of the study, told IFLScience.
Kepler-438b is the exoplanet with the highest Earth Similarity Index: It is only marginally bigger and heavier than Earth, with an average surface temperature of 3°C (37.4°F). The planet is very close to its star, orbiting at a distance of 24 million kilometers (15 million miles), which makes the flares and CMEs much more dangerous.
“The likelihood of a coronal mass ejection occurring increases with the occurrence of powerful flares, and large coronal mass ejections have the potential to strip away any atmosphere that a close-in planet like Kepler-438b might have, rendering it uninhabitable," Chloe Pugh, co-author of the study, said in a statement. "With little atmosphere, the planet would also be subject to harsh UV and X-ray radiation from the superflares, along with charged particle radiation, all of which are damaging to life."
If Kepler-438b possesses a magnetic field, there is a possibility that it has been shielded from some of the most destructive activity of its star. Based on current data from the Kepler telescope, it’s not possible to confirm or deny the presence of an atmosphere around the exoplanet, though. Kepler-438b continues to be a fascinating object, but with this latest discovery, the search for a second Earth is still wide open.